Modulus-mismatch strategy optimized lightweight refractory high-entropy alloys for superior synergy of mechanical properties and thermostability

Lightweight refractory high-entropy alloys (LRHEAs) have received significant attention due to their excellent strength-plasticity matching. Generally, its strengthening mechanism mainly comes from solid solution strengthening caused by atomic radius mismatches, but excessive atomic radius mismatch can reduce the phase stability of solid solution and easily generate precipitated phases to reduce the plasticity. Here, we present a strategy to enhance the shear modulus mismatch while improving the mechanical properties and phase stability of LRHEAs. We chose the TiZrVNbAl system as the LRHEAs model. The addition of Mo resulted in a modulus mismatch induced strength contribution of 564 MPa, which accounts for ∼57 % of the total strength. Compared to the alloy without Mo, the strength increased by ∼42 % without any loss of ductility. More importantly, the addition of Mo significantly reduces the diffusion coefficient of the main element and realizes the effective kinetic suppression of the precipitated phase. This enables the alloy to avoid brittle precipitate generation even after aging at 500 °C for 5 h, and hence the excellent mechanical properties are well kept. Additionally, the strength of the LRHEA is increased by more than two times at 700 °C, demonstrating higher high temperature performance compared to RHEAs with tensile ductility. Utilizing the shear modulus mismatch strategy can effectively enhance the solid solution strengthening effect, improving the comprehensive mechanical properties of the alloy at room temperature and high temperature, while also improving phase stability. This provides a new approach to developing structurally stable high-performance alloys.